This invention relates to a planetary gear apparatus suited to be used as a differential gear mechanism of a vehicle and the like.
In general, a planetary gear apparatus of this type includes an inner gear, a sun gear which is disposed with an axis thereof aligned with that of the inner gear, a planetary gear disposed between and in parallel with the inner gear and the sun gear, and a carrier having a receiving hole for rotatably receiving the planetary gear. The carrier is provided with two releasing parts for releasing the receiving hole to the outside. One and the other part of an outer peripheral part of the planetary gear are exposed to the outside from the respective releasing parts. The planetary gear is engaged with the inner gear and sun gear at its respective parts which are exposed to the outside from the respective released parts (see Japanese Patent Application Laid-Open No. H04-312247 and Japanese Patent Application Laid-Open No. H09-112657).
However, the above-mentioned conventional planetary gear apparatus has such problems that the planetary gear is heavily vibrated during its rotation operation, and the planetary gear and carrier are seriously damaged. After studying very hard about those problems, it became clear for the present inventor(s) that the number of teeth of the planetary gear, which teeth contact an end edge facing an releasing part of an inner peripheral surface of the receiving hole simultaneously, is less than one. The detail of the cause will be described later.
In order to solve the above problems, the features of the present invention reside in a planetary gear comprising an inner gear, a sun gear disposed at an inner side of the inner gear with an axis thereof aligned with that of the inner gear, a planetary gear disposed between and in parallel relation with the inner gear and the sun gear and adapted to transmit rotation between the inner gear and the sun gear, and a carrier relatively rotatably disposed with an axis thereof aligned with that of the inner gear and having a receiving hole for receiving the planetary gear such that the planetary gear can rotation on its own axis, the carrier being provided with two releasing parts extending along the axis of the receiving hole and adapted to intercommunicate an interior part and an exterior part of the receiving hole, one of the two releasing parts being formed at an outer side and the other at an inner side in the radial direction of the carrier, an outer peripheral part of the planetary gear being exposed to the outside of the receiving hole through the two releasing parts, wherein a helical gear is used as the planetary gear, and at least one tooth of the planetary gear is capable of contacting an end edge facing the releasing parts at the inner peripheral surface of the receiving hole irrespective of a rotational position of the planetary gear.
In this case, it is preferred that the at least two teeth of the planetary gear are capable of contacting an end edge facing the releasing parts at the inner peripheral surface of the receiving hole irrespective of a rotational position of the planetary gear.
It is also preferred that at least one tooth of the planetary gear is capable of simultaneously contacting two end edges of an inner peripheral surface of the receiving hole facing two sides of the releasing parts irrespective of a rotational position of the planetary gear.